Grid relief in CMP polishing pad to accurately measure pad wear, pad profile and pad wear profile

ABSTRACT

A method and apparatus for measuring wear of the thickness of a chemical mechanical polishing pad are provided. The apparatus includes a chemical mechanical polishing pad having a plurality of reliefs in a main polishing surface for determining wear of the pad. In one aspect, the pad reliefs comprise through-holes in the pad or extend partially through a thickness of the pad. The method for measuring wear of the thickness of a chemical mechanical polishing pad includes providing a plurality of reliefs in a main polishing surface of the pad and measuring a distance from the main polishing surface to a bottom surface of each of a plurality of the reliefs.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of co-pending U.S. patentapplication Ser. No. 09/826,419, filed Apr. 5, 2001, which claimsbenefit of U.S. Provisional Patent Application Serial No. 60/195,523,filed Apr. 7, 2000. Each of the aforementioned related patentapplications is herein incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an apparatus for performingchemical mechanical polishing (CMP) during manufacture of asemiconductor device on a semiconductor substrate. The present inventionhas particular applicability to monitoring CMP to ensure processquality.

[0004] 2. Description of the Related Art

[0005] Chemical mechanical polishing (CMP) is a conventionalsemiconductor device manufacturing technique employed to flatten films,such as interlayer insulating films, and to form metal plugs andinterconnections in multiple-layer interconnection processes. As shownin FIG. 1, in a typical CMP apparatus, a rotating holder 12 supports awafer 14, while a rotating platen 11 holds a polishing pad 17, usuallyvia an adhesive. A first supply nozzle 15 drips a polishing solution inthe form of an abrasive slurry onto polishing pad 17, and a secondsupply nozzle 16 drips water onto polishing pad 17 for rinsing.Typically, pad 17 is larger than wafer 14 (e.g., pad 17 has a 10-inchradius and wafer 14 has an 8-inch diameter), and the wafer and pad arerotated in the same direction at the same speed while they are urgedagainst each other, to effect polishing of wafer 14. Additionally, wafer14 is typically moved across pad 17 during polishing, but kept away fromthe center of pad 17 to avoid unwanted torque effects and unevenpolishing. As a result, the footprint of polishing pad 17 on wafer 14during polishing is equivalent to a belt, and the same amount ofmaterial is removed across the surface of wafer 14.

[0006] As wafer 14 is swept across pad 17 during polishing, someportions of pad 17 may wear to a greater extent than other portions ofpad 17. Pad wear is also affected by “conditioning” of the pad, aprocedure wherein the polishing pad surface is restored to an abrasivecondition after being glazed (i.e., made smoother and less abrasive) bynormal use. The unevenness of pad wear is expressed graphically in FIG.2 as a “wear gradient” line W₁. Depending on the conditioning of thepad, wear is likely to be non-uniform; e.g., pad wear may increasetowards the outer radius of pad 17, while the center may not wear atall. This is in contrast to the ideal wear gradient W₂, which is evenacross the pad. Disadvantageously, if pad 17 is worn unevenly, whetherdue to polishing or conditioning, wafer 14 will see a pressure gradientacross pad 17 (e.g., less pressure or “load” towards the edge of pad17), resulting in less polishing at the edge of pad 17, and unevenpolishing of the wafer surface. Moreover, even if the CMP processparameters are optimized so pad wear is even, the rate of wear changesfrom pad to pad. Thus, it is desirable for process control purposes tomonitor pad thickness in situ.

[0007] Prior art techniques for monitoring the condition of CMPpolishing pads include removing the pad from the platen, cutting a stripfrom the pad, and measuring its thickness. A more advanced,non-destructive pad testing methodology comprises running a stylusacross the polishing pad while it is attached to the platen to measurethe pad's thickness. This method requires that the stylus be stablymounted relative to the pad and platen, and requires that the stylus runacross the pad in a reproducible manner, since the stylus must be runacross the pad before polishing, and again after polishing, and itsmeasurements compared. However, the reproducibility necessary foraccurate measurements can be difficult to achieve. During polishing, thepad is abraded, exposed to the slurry and exposed to water, resulting indifferent frictional properties across the pad that cause the stylus torock and produce inconsistent measurements. Furthermore, the relativelyrigid polishing pad is often “stacked” with a compliant foam underlayerbetween the pad and the platen. The underlayer can swell duringoperation as it absorbs liquids such as water and/or slurry, and canbecome compressed during polishing due to the pressure applied betweenthe pad and the wafer, thereby adversely affecting the accuracy of padthickness measurements.

[0008] An improved methodology for inspecting pad wear is disclosed incopending U.S. application Ser. No. 09/338,357, filed Jun. 22, 1999,wherein a pad wear profile is generated using a contactless displacementsensor, such as a laser displacement sensor. The method of the copendingapplication solves some of the problems inherent in stylus-type padmeasurement techniques; however, the measuring apparatus must still bestably mounted relative to the pad, and reproducibility of measurementsis still problematic due to stacking of the pad on a compliantunderlayer.

[0009] As semiconductor devices become more complex and process windowsshrink, the need for in-process monitoring of manufacturing techniquessuch as CMP has become increasingly critical. There exists a need for asimplified, accurate methodology for monitoring CMP pad wear and padwear profile, thereby reducing manufacturing costs and increasingproduction throughput.

SUMMARY OF THE INVENTION

[0010] An aspect of the present invention is a simplified method ofmonitoring pad wear, pad profile and pad wear profile that does notdepend on location of the pad or location of the measuring device foraccuracy.

[0011] Additional aspects and other features of the present inventionwill be set forth in part in the description which follows and in partwill become apparent to those having ordinary skill in the art uponexamination of the following or may be learned from the practice of theinvention. Aspects of the invention may be realized and obtained asparticularly pointed out in the appended claims.

[0012] According to the present invention, the foregoing and otheraspects are achieved in part by a chemical mechanical polishing padhaving a plurality of reliefs in a main polishing surface fordetermining wear of the pad.

[0013] Another aspect of the present invention is a method for measuringwear of the thickness of a chemical mechanical polishing pad, the methodcomprising providing a plurality of reliefs in a main polishing surfaceof the pad, and measuring a distance from the main polishing surface toa bottom surface of the reliefs.

[0014] Additional aspects of the present invention will become readilyapparent to those skilled in this art from the following detaileddescription, wherein only the preferred embodiment of the presentinvention is shown and described, simply by way of illustration of thebest mode contemplated for carrying out the present invention. As willbe realized, the present invention is capable of other and differentembodiments, and its several details are capable of modifications invarious obvious respects, all without departing from the invention.Accordingly, the drawings and description are to be regarded asillustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Reference is made to the attached drawings, wherein elementshaving the same reference numeral designations represent like elementsthroughout, and wherein:

[0016]FIG. 1 illustrates a conventional CMP apparatus.

[0017]FIG. 2 graphically illustrates CMP pad wear gradient.

[0018]FIG. 3A is a top view of a CMP polishing pad according to anembodiment of the present invention.

[0019]FIG. 3B is a cross-sectional view of a CMP polishing pad accordingto an embodiment of the present invention.

[0020]FIG. 3C is a cross-sectional view of a CMP polishing pad accordingto an embodiment of the present invention.

[0021]FIG. 4 is a top view of a CMP polishing pad according to anembodiment of the present invention.

[0022]FIG. 5 is a top view of a CMP polishing pad according to anembodiment of the present invention.

[0023]FIG. 6 is a flow chart illustrating the methodology of anembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0024] Conventional methodologies for monitoring CMP polishing pad weareither require destruction of the pad, require accurate placement of thepad and measuring device for accuracy, and/or can be adversely affectedby the condition of the pad underlayer. The present invention addressesand solves these problems stemming from conventional techniques,enabling monitoring and control of the CMP process to maintain evenpolishing over a range of changing process conditions.

[0025] According to embodiments of the present invention, a plurality ofstrategically located reliefs are provided in the polishing surface of aCMP polishing pad, the reliefs extending either partially or completelythrough the thickness of the pad. The reliefs may include trenches inthe pad that have an upper “lip” at the surface of the pad and a lower“ledge” at the bottom of the relief. In operation, the reliefs arescanned, as by a conventional stylus-type instrument or a conventionalcontactless displacement sensor such as a laser. When the stylus orlaser scans it, the instrument detects one flat surface (the lip) andthen detects another flat surface (the ledge), thus enabling theinstrument to accurately measure the depth of the relief independent ofthe position of the pad or the position of the measuring hardware. Thereliefs are scanned before the pad is used and then scanned again afteruse to measure the difference in the depth of the reliefs, therebyindicating pad wear. Such information is then used to monitor total padwear, and to generate a pad profile and a pad wear profile.

[0026] The present invention provides accurate pad thicknessmeasurements quickly and easily, thereby enabling the pad wear profileto be closely monitored; e.g., measured every 50-100 wafers, in acost-effective manner. Consequently, process monitoring can be improvedby utilizing the present invention in a feedback loop to reducevariation in process quality, to indicate that process changes arerequired, and to modify conditioning residence times, conditioning loadand/or relative conditioning velocity as a function of pad location.

[0027] An embodiment of the present invention is illustrated in FIGS.3A-3C. Referring to FIGS. 3A-3C, a plurality of reliefs 310 are providedin a predetermined pattern in a conventional polishing pad 300 having athickness t, such as the IC1000 polishing pad available from RodelCorporation of Phoenix, Ariz. Reliefs 310 extend partially through pad300 to a depth d as shown in FIG. 3B or, in an alternative embodiment ofthe present invention shown in FIG. 3C, reliefs 320 extend completelythrough pad 300, exposing underlayer 330. Reliefs 310, 320 can be formedby cutting, embossing or machining pad 300, or are integrally moldedwith pad 300. Additionally, through-hole type reliefs 320 can be formedby punching or stamping. Reliefs 310, 320 have a length 1, width w andshape (e.g., rectangular, square, triangular, circular) such that theycan be probed with a conventional stylus-type instrument such as an LVDT(Linear Velocity Differential Transformer) available fromLucas/Signatone Corp. of Gilroy, Calif., or a conventional laserinterferometer such as available from MTI Instruments of Albany, N.Y.Reliefs 310, 320 are spaced apart a distance s such that a quantity ofreliefs adequate to indicate pad wear accurately are provided. Forexample, when pad 300 has a thickness t of about 50 mil, rectangular orsquare reliefs 310 are formed to a depth d of about 30 mil, width w ofabout 20 mil to about 500 mil, and length l of about 20 mil to about 500mil, and are spaced about 250 mil to about 10,000 mil apart.

[0028] The trench-type reliefs 310 of the embodiment of FIG. 3B can beutilized rather than the through-hole type reliefs 320 of FIG. 3C if astylus probe is used having a limited range of travel. However, a laserprobe can adequately handle deep reliefs and through-hole type reliefs320. Through-hole reliefs 320 are advantageous in that they enabledirect measurement of the physical pad dimension t, although accuracymay be affected by the necessity of measuring to the compliantunderlayer 330 which, as discussed above, is compressible, and may swelldue to absorption of liquid. Trench-type reliefs 310 avoid dependence onunderlayer 330 since the measurement of depth d of trench-type reliefs310 is made from one stable surface 300 a to another stable surface 300b.

[0029] Referring to FIGS. 3A, 4 and 5, reliefs 310, 410, 510 can bearranged in a pattern enabling pad wear to be measured at a plurality oflocations on pad 300, 400, 500, respectively, such that pad wear profileis determinable as a function of pad radius (e.g., to determine if thepad is wearing more at the outer edge due to sweeping of the waferrelative to the pad during polishing). Furthermore, reliefs 310, 410,510 can be distributed to also enable development of a two-dimensionalpad wear profile; for example, to enable monitoring of whether oneportion of pad 300, 400, 500 is wearing at a higher rate than anotherportion. Such information is useful in determining the evenness of theplaten (not shown), the evenness of the pad, the presence of air bubblesunder the pad, and the consistency of adhesion between the pad andplaten.

[0030] Referring again to FIG. 3A, reliefs 310 are arranged along adiameter of pad 300. Thus, the wafer (not shown) “sees” a line ofreliefs 310 when it is being polished, and a pad wear profile as afunction of pad position is generated using the methodology of thepresent invention. FIG. 4 illustrates an alternative embodiment of thepresent invention, wherein reliefs 410 are provided in pad 400 in aspiral pattern. A wafer being polished by pad 400 sees only one relief410 at a time (rather than the line of reliefs 310 seen by a wafer beingpolished by pad 300). Thus, the spiral relief pattern distributes padstress originating from reliefs 410 across the surface of pad 400,avoiding stress concentrations that may arise from the line of reliefsof pad 300. When employing a spiral pattern of reliefs as shown in FIG.4, the combination of the spiral pattern, rotational speed and wafersweep can be chosen to avoid having the pattern look like a line to thewafer.

[0031] Referring now to FIG. 5, in a further embodiment of the presentinvention, the pattern of reliefs 510 is a non-symmetrical pseudo-randomspiral distribution. This distribution is typically computer-designedand mapped such that the location of each relief 510 is known, and sothat reliefs 510 are advantageously located to accurately measure padwear and pad wear profile without introducing undesirablestress-inducing symmetry into the system.

[0032] The methodology of an embodiment of present invention will now bedescribed with reference to FIGS. 3A, 3B and the flow chart of FIG. 6.At step 610, the reliefs of a polishing pad (e.g., reliefs 310 of pad300 in FIGS. 3A and 3B) are scanned, as by a laser interferometer orLVDT stylus, to measure the depth of the reliefs, such as the depth d ofrelief 310. Polishing pad 300 is then used to polish a predeterminednumber of wafers at step 620; for example, 50 wafers. Next, at step 630,reliefs 310 are scanned again by the laser or LVDT stylus to measuretheir depth d. The depth measurements of steps 610 and 630 are used tocalculate the pad wear at each relief 310 (see step 640), and the padwear measurements are used at step 650 to generate a pad wear profile.The calculations of steps 640 and 650 can be carried out electronicallyby a computer processor.

[0033] If the pad wear is unacceptably fast or if the profile isunacceptably non-flat, at step 660 the process parameters are changedfor the next group of wafers to be processed by pad 300, as desired bythe user. For example, to improve the flatness of the pad wear profile,one or more of the following variables is typically adjusted:

[0034] conditioning residence time, load and/or relative velocity as afunction of pad location or pad thickness

[0035] residence time of the wafer over different parts of pad 300(e.g., more or less time at the edge of pad 300)

[0036] load (pressure) on the wafer vs. location on pad 300 or thicknessof pad 300

[0037] rotational velocity of the wafer vs. location on pad 300 orthickness of pad

[0038] sweep range of wafer vs. thickness of pad 300 or location on pad300 (e.g., if a problem occurs at the edge of pad 300, avoid polishingwith edge)

[0039] retaining ring pressure vs. pad thickness

[0040] Thus, the present invention provides a feedback loop to monitorpad flatness, platen flatness, consistency of pad to platen adhesion andthe presence of air bubbles between pad and platen, and improve thequality of the CMP process.

[0041] The present invention is also useful for controlling pad flatnessto attain an ideal pad wear gradient after process parameters thataffect pad wear have been changed. For example, pad wear and pad wearprofile can be measured by the techniques of FIG. 6 when a differentslurry, conditioner or pad is introduced, or after a mechanical changeto the appaatus such as a different size pad or wafer.

[0042] Still further, the present invention extends the useful life of apolishing pad after pad wear problems have occurred. For example, sincethe pad wear rates and wear profile is determinable by the presentinvention, excessively worn areas of the pad can be avoided while “good”areas are used for polishing, rather than discarding the pad.Alternatively, the above-discussed variables can be adjusted based onthe pad wear profile or wear rate to maintain the polishing rate at aproblematic portion of the pad.

[0043] The present invention is applicable to the manufacture of varioustypes of semiconductor devices, particularly high-density semiconductordevices having a design rule of about 0.18μ and under.

[0044] The present invention can be practiced by employing conventionalmaterials, methodology and equipment. Accordingly, the details of suchmaterials, equipment and methodology are not set forth herein in detail.In the previous descriptions, numerous specific details are set forth,such as specific materials, structures, chemicals, processes, etc., inorder to provide a thorough understanding of the present invention.However, it should be recognized that the present invention can bepracticed without resorting to the details specifically set forth. Inother instances, well known processing structures have not beendescribed in detail, in order not to unnecessarily obscure the presentinvention.

[0045] Various embodiments of the present invention and but a fewexamples of its versatility are shown and described in the presentdisclosure. It is to be understood that the present invention is capableof use in various other combinations and environments and is capable ofchanges or modifications within the scope of the inventive concept asexpressed herein.

1. A chemical mechanical polishing pad having a plurality of reliefs ina main polishing surface for determining wear of the pad, wherein thereliefs are disposed in a predetermined pattern such that the wear ofthe pad is determinable as a function of pad radius.
 2. The pad of claim1, wherein the reliefs extend partially through a thickness of the pad.3. The pad of claim 2, wherein the pad is round.
 4. The pad of claim 3,wherein the plurality of reliefs in have a rectangular, square,triangular or round shape.
 5. A chemical mechanical polishing pad havinga plurality of reliefs in a main polishing surface for determining wearof the pad, wherein the reliefs comprise through-holes in the pad. 6.The pad of claim 5, wherein the reliefs are distributed in apredetermined pattern to enable monitoring the pad wear as a function ofpad radius.
 7. The pad of claim 6, wherein the predetermined pattern isconfigured to enable monitoring of the pad wear to discern whether twoor more regions of the pad are wearing at different rates.
 8. The pad ofclaim 6, wherein at least some of the reliefs are individually monitoredto establish a wear pattern specific to a pattern of at least some ofthe reliefs.
 9. The pad of claim 6, wherein the pad is round.
 10. Thepad of claim 9, wherein the plurality of reliefs in have a rectangular,square, triangular or round shape.
 11. A chemical mechanical polishingpad having a plurality of reliefs disposed in a predetermined patternthereon, wherein the predetermined pattern is configured to indicate thewear of at least one region of the pad with respect to the pad radius.12. The pad of claim 11, wherein the predetermined pattern is configuredto enable monitoring of the pad wear to discern whether two or moreregions of the pad are wearing at different rates.
 13. The pad of claim11, wherein the predetermined pattern is selected from inline, spiral,non-symmetrical pseudo-random, and combinations thereof.
 14. The pad ofclaim 13, wherein the pad is round.
 15. The pad of claim 14, wherein theplurality of reliefs in have a rectangular, square, triangular or roundshape.
 16. A chemical mechanical polishing pad having a plurality ofreliefs in a main polishing surface for determining wear of the pad,wherein the reliefs have a rectangular, square, triangular or roundshape.
 17. The pad of claim 16, wherein the pad is round.
 18. A chemicalmechanical polishing pad having a plurality of reliefs in a mainpolishing surface for determining wear of the pad, wherein the reliefscomprise through-holes in the pad or extend partially through athickness of the pad.
 19. The pad of claim 18, wherein the pad is round.20. The pad of claim 19, wherein the plurality of reliefs in have arectangular, square, triangular or round shape.